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MSP-FET: red led when connecting to externally powered device

adevries
Intellectual 945 points
Part Number: MSP-FET

Hello TI Forum,

I have an MSP-FET Flash Emulation Tool that I use to program MSP430 micrcontrollers on custom, externally powered boards. Oftentimes I will leave the tool plugged in to my computer, connect the 14-pin idc connector to the custom PCB, and then turn on the external power to the board. However, I've noticed that if the MSP-FET is plugged in to my computer and the unpowered external board, the red led illuminates by itself (no green LED). I've also noticed there is voltage on the RST pin (and some other pins) that cycles up to 1.8V then goes back to 0V, repeating.

Once I externally power my custom pcb, the red led turns off, the green led turns on, and I can program it no issue. But I'm a little concerned with the behavior I'm seeing. I couldn't find any instructions that say "you must plug in the MSP-FET after turning on external power", so I've been assuming it doesn't matter if the FET tool is plugged in before applying external power. But, since I have the pin connections set up for programming an externally powered device, I'm surprised to see the tool injecting power into the target board. Is this expected behavior? Is it possible I have a faulty MSP-FET?

Thanks in advance for any assistance!

  • 0
    TI__Mastermind 20025 points

    Hi Thanks for your question!

    according to 5.6.4 LED Signals of MSP Debuggers User's Guide (Rev. O). I think MSP-FET works normally.

    >> Once I externally power my custom pcb, the red led turns off, the green led turns on, and I can program it no issue.

    >> However, I've noticed that if the MSP-FET is plugged in to my computer and the unpowered external board, the red led illuminates by itself (no green LED).

  • 0 in reply to Xiaodong LI
    Intellectual 945 points

    Hi Xiaodong,

    Thanks for the reply. Can you explain why the MSP-FET would inject power into a board that is supposed to be externally powered? And why it would think an error has occurred when plugged into an unpowered board?

    Is it expected behavior to have the MSP-FET do this?

  • 0 in reply to adevries
    TI__Mastermind 20025 points

    Hi

    General speaking, if the external board is not power, green LED can be off because An error has occurred; for example, target VCC over current. Unplug MSP-FET from target, and cycle the power off and on. Check target connection, and reconnect MSP-FET. this is related with user's board.

    At the same time, 1.8V then goes back to 0V, repeating on RST pin and other pins, this is the abnormal signal for example maybe it is the noise from the user's board. Could you please help to comment JTAG or SBW you are using insides 14-pin connector? which pins are used in the 14-pin connector?

    Thanks!

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